A machine tool uses guide rails to limit moving directions of its components. However, as the hours of use accumulate, the guide rails might be worn or damaged. For example, scratches or pits may appear on the guide rails. Such damages may cause undesired high-frequency vibrations that adversely affect the operation of the machine tool, creating faulty products. Severe damages may even cause a breakdown of the machine tool or injury of an operator of the machine tool. In order to prevent formation or aggravation of these damages, the machine tool (especially the guide rails) should be oiled in time.